In general, Ethernet is a point-to-point communication technology. More complex networks are created by using layer 2 (according to the ISO/OSI stack) bridges (also called switches). Switches enable the definition of complex network topologies and offer many services including the basic relying of frames (the basic Ethernet communication element) from one source node to multiple destinations, and more complex operations such as channel bandwidth allocation, network partitioning via virtual LANs (VLANs) and traffic prioritization.
The bandwidth requirements of modern and future automotive applications are posing a relevant challenge to current in-vehicle networking (IVN) technologies such as Controller Area Network (CAN) and FlexRay. Thanks to the latest development of the Ethernet technology, a 100 Mbps Ethernet link can now be implemented and a 1 Gbps link will be available in near future. The automotive Ethernet technology is based on an unshielded twisted pair of copper wires while limiting the EMC (electromagnetic compatibility) requirements below the threshold imposed by the regulatory automotive standards. Switched Ethernet networks have been implemented in the automotive market for supporting bandwidth-intensive applications such as backbones interconnecting various domains, infotainment and surround-view applications.
In the automotive environment, EMC requirements are crucial and have to be controlled. The unshielded twisted pair of copper wires is not only subjected to interferences but is a source of EME (electromagnetic emission) at the same time. The source of such EME depends inter alia on the mode conversion function of the transfer modes (common mode and differential mode) and the magnitude of the differential signals. Differential mode signals can be partly converted to common mode signals along the transmission path of a data link and vice versa.
It is immediately understood that there is a need to control or minimize EME emitted by communication links in an automotive environment.